Coating method

ABSTRACT

In coating a coating composition on a web by a bridge of the coating composition between a coating applicator and the web, a gas blowing slot is formed at the side of the coating applicator into which the web enters to remove air or dust carried on the surface of the entering support and to provide a reduced pressure space at the back side of the bridge so that the bridge is maintained stable when the coating speed is increased.

United States Patent Ishiwata et al.

[ 1 Feb. 8, 1972 [54] COATING METHOD [72] Inventors: Mamoru lfliiwata;l-luruya Aldo, both of Kanagawa, Japan [73] Assignee: Fuji Shashin FilmKabushiki Kaisha,

Kanagawa, Japan [22] Filed: June 24, 1969 [21] Appl. No.: 869,407

Related us. Application um [62] Division of Ser. No. 635,540, May 2,1967, Pat. No.

[52] US. Cl ..ll7/47, 117/34, 117/119 [51} Int. Cl ..B44d 1/02 [58]Fieldot'Search ..ll7/47,34, 120, 119; 118/410 [56] References CitedUNlTED STATES PATENTS 2,681,294 6/1954 Beguin ..l17/34 2,761,791 9/1956Russell ..1 17/34 2,795,522 6/1957 Johns 2,815,307 12/1957 Beck3,206,323 9/1965 Miller et a1.

3,220,877 11/1965 Johnson ..1 17/120 Primary Examiner-William D. MartinAssistant Examinerwilliam R. Trenor AttorneySughrue, Rothwell, Mion,Zinn and Macpeak [57] ABSTRACT In coating a coating composition on a webby a bridge of the coating composition between a coating applicator andthe web, a gas blowing slot is formed at the side of the coatingapplicator into which the web enters to remove air or dust carried onthe surface of the entering support and to provide a reduced pressurespace at the back side of the bridge so that the bridge is maintainedstable when the coating speed is increased.

2 Claims, 2 Drawing PAIENTEDFEB 8 I972 N ORS MAMORU 'ISHIWATA AKIQ UYACOATINGMETHOD CROSS REFERENCE TO RELATED APPLICATION This application isa division of application Ser. No. 635,540 filed May 2, 1967 and now US.Pat. No. 3,503,370.

This invention relates to an apparatus for applying a coatingcomposition to one side of a continuously moving web.

For applying a coating composition to one side of a continuously movingweb. it is known to use a slide hopper, an extrusion hopper, a doctorblade, and the like as a coating applicator. When coating of a thinlayer at high speed is carried out by one of these known means, a bridgeor layer of the coating composition between the coating applicator andthe support is broken by the shearing force of the moving support or byan air film carried by the surface of the moving support, and a uniformcoafing cannot be obtained.

Moreover, with the prior art coating applicators, dust on the surface ofthe support attracted by electrostatic force are often transferred tothe edge of a coating applicator when the support passes through thecoating applicator, resulting in undesirable influence upon the coatingbridge and the forming of stripes in the coating.

For overcoming these difiiculties, this invention provides formaintaining a lower pressure on the web inlet side of the coatingapplicator than on the outlet side to prevent breaking the bridge due tothe air film carried on the surface of the sup port. Otherwise breakingof the coating bridge cannot be adequately prevented when the support istravelling at high speed. The negative pressure on the inlet side of theapplicator also eliminates the dust problem.

The coating apparatus of the present invention will now be illustratedin the accompanying drawing, in which FIGS. 1 and 2 are schematic sidesectional elevation views illustrating two embodiments of thisinvention.

Referring to the drawing, a web 1 to be coated moves continuously,around a backup roller 2, facing a coating applicator 3 such as a slidehopper (FIG. 1) or an extrusion hopper (FIG. 2).

A slot 4 is formed adjacent to a reduced pressure space 6 and isconnected to a compressed gas chamber 5 for blowing a gas jet tangentialto the web on roller 2 and opposite the direction of movement of theweb. The clearance of the slot 4 may be controlled if necessary. Reducedpressure space or chamber 6 is provided at the entrance of the web tothe coating applicator and behind the coating bridge B. A blower 7 isconnected to the compressed gas chamber 5 for supplying a gas of avolume and pressure necessary to provide a gas jet from slot 4. In FIG.1 a gas exhausting means 9 having a capacity corresponding to the jetgas is connected to a suction chamber 8.

In operation, if the clearance of slot 4 and the pressure of compressedgas chamber 5 are selected so that the speed of the gas jet at theoutlet of the gas-blowing slot 4 may be maintained at a desired value(preferably to 0.5-1.0 mm. in clearance and more than 200 mm. watergauge in pressure respectively), t air film carried by the travellingsupport is removed by the gas jet from slot 4 and dust adhered to thesurface of the support is also removed by the gas jet. At the same time,the pressure of space 6 is maintained at a suitable reduced value by theaspiration action of the gas jet, whereby the bridge B of the coatingcomposition can be stabilized and the coating can be uniformlyaccomplished.

The gas generally used is air, although an inert gas, steam, solventvapor or gas containing a small amount of surface active agent may beused, if necessary. A surface active agent may be contained in the gas,in which case air on the surface of the web is replaced with the gas andthe temperature and physico-chemical properties of the-web are changedso that the web surface may be endowed with antistatic property and theadhesion of the coating composition to the web is enhanced.

As evident from the foregoing, this invention provides an improvedcoating apparatus in which coating of a thin laiyer can be carned out ata high speed, the prob ems due to ust adhered to the surface of the webcan be overcome, the adhesive force of a coating composition to thesupport can be enhanced and the coating bridge thereof between thesupport and device can be maintained stable to accomplish rapid anduniform coating.

Further, the gas-blowing slot is positioned adjacent the coatingapplicator at the web entrance side so that the gas jet is substantiallytangential to the surface of the travelling support.

When coating is conducted by using the improved coating apparatus of thepresent invention, the following advantages are obtained.

Dust carried on a travelling support or web is removed by the high speedgas jet blown from the gas blowing slot and at the same time the backside of the bridge of a coating composition forrned between a coatingdevice and the travelling support is maintained at a lower pressure,which enables the uniform and stable coating of a thin layer with a highspeed that has never been attained by conventional means.

The invention has been described above about a specific embodiment, butit should be understood that the invention is not limited to the formand construction of the illustrated apparatus.

What is claimed is:

l. A method for coating a web moving around a backup roll comprising a.applying a bridge of coating material to said web on said roll from anapplicator disposed in close proximity to said roll b. directing a gasjet from said applicator tangentially against said web on said roll in adirection opposite to the direction of travel of said web at a pointupstream from said bridge relative to the direction of travel of saidweb to provide a negative pressure on the back side of the bridge and onthe surface of the web between said bridge and said point of gas jetapplication while simultaneously cleaning said web and providing apositive holddown force on said web.

2. A method as set forth in claim 1 further comprising c. adding asurface treatment agent to said gas jet to provide for simultaneoussurface treatment of said web along with the application of said gasjet.

2. A method as set forth in claim 1 further comprising c. adding a surface treatment agent to said gas jet to provide for simultaneous surface treatment of said web along with the application of said gas jet. 